How do I stay calm with abusive passengers as flight crew?

Serving most passengers well and still being rattled by the abusive and the entitled ones is not a weakness. It is what happens when you keep your humanity in a job that sometimes strips others of theirs. The calm passengers cost you nothing; the abusive ones reach for something in you, and feeling that is the price of still caring. It does not mean you are failing. What helps is remembering that their behavior is a report on them, not on you. The entitled and the abusive are usually carrying their own smallness, fear, or bad day into that cabin, and you happen to be in front of them. Their cruelty is theirs. You do not have to accept it as truth about yourself, and you do not have to absorb it to serve well. You can stay courteous and stay untouched at once. Build one small protection: after a bad encounter, take a breath and silently set it down before the next passenger, so their poison does not travel with you. Keep your standard of care high and your sense of self separate from their behavior. You give a real service. Do not let the worst of them define the worth of it. Guard the person underneath the uniform.